TRL Dude or Joule 150 MKII for Major Pre Upgrade

Tim, sounds like the single-ended preamp has a ground loop problem when working into the balanced amp via an adapter, the loop being broken, as might be expected, when the transformer is used.

An adapter-based approach that I suspect would provide better results, although probably not as good as the transformer-based approach, would be to connect RCA male to XLR male adapters at the preamp outputs, and run XLR cables from there to the amp. That would essentially be equivalent to the arrangement shown in Figure 2.1 of this Jensen paper on interfacing balanced and unbalanced equipment.

With respect to using the transformer, I wouldn't necessarily conclude that you have to stay below 2K output impedance for the preamp, given that your amp has an input impedance of 100K. It seems conceivable to me that the 2K figure in the datasheet is based on the assumption of a 20K load, just as the input impedance spec is based on that assumption.

However, when deciding on whether to purchase this single-ended Dude, I called them again this past week and was told the input impedance would be a maximum of 25K ohms, as shown on the data sheet.

My guess is that the person you were speaking with was not Mr. Whitlock :-)

Maybe another phone call is in order.

Yes, that would seem clear.

On the other hand, you could buy one of Ralph's preamps, and the issues would all be moot :-)

(I have no affiliation).

Best regards,
-- Al

The Dude as an output impedance of around 5k ohms. I am having the same noise problem in my system with an Aesthetix Atlas hybrid amp and my Dude preamp. The Atlas has both xlr and RCA inputs however. I get a buzz with both the Dude and a passive preamp -
Lightspeed Attenuator. Seems both of our amps may be very picky regarding single ended preamps and ic's? Al has tried to help me figure out my issue, but I still have a buzz - slight buzz on both speakers. Sounds like some sort of ground loop issue to me.

Strange for sure..For me the buzz only came when I changed speakers from active to passive. No buzz with active speakers, buzz with passive.

System sounds great so I live with it. Can't hear it 10 feet back.

I tried adaptors like you with pins 1 and 3 tied, still a buzz. I purchased an ic that goes from RCA to xlr with 1 and 3 combined, still have a buzz.

I am getting some kind of ground loop issue when my ic's are connected. Any ic's. I may try your transformer answer, but now wonder if their will be an input impedance mismatch with my pre and the Jensen transformer? The Dude has 5k ohms of output impedance.

Grannyring, I have an extra transformer since I went from a two-channel transformer box (both L and R channels in one box) to mono transformers (two boxes) when I moved my monoblocks further apart (although they are now closer together again). The balanced cables out of the transformers should be no more than 1M long. The ones I use are about 2 feet long. To use the one-box version, your monoblocs must be reasonably close together.

I had offered to let another member try the transformers. Since he is not having the buzz issue and I do not think he needs/wants to try the transformers right now, maybe you would like to try them and see if they help. This would be interesting information for me too, because then I would learn whether a single-ended Dude might work for me.

My plan earlier this week was to try the single-ended (SE) Dude that was up for sale on this site and if I liked it to go ahead and order a balanced Dude while continuing to use the SE Dude. I planned to use the SE version for the 3 months it takes TRL to make these and then sell it after I received my new balanced Dude. I declined to buy the SE Dude after my research indicated the 5K ohms output impedance may not work with the transformers. However, Almarg is correct, I do not believe I spoke with Bill Whitlock when I called Jensen last week.

Almarg, I know Ralph's preamps are fully balanced and would work properly with my set-up. While I respect Ralph and his company immensely, I just didn't care for the sound of the Atma-Sphere preamp that I owned some years ago. It was a tricked out MP-3 with teflon, regulated power, and Caddocks. I am aware of an Atma-Sphere preamp for sale now that is called an MLS-1 Linestage, which is apparently a one-box precurser to the MP-1. I know it is old because it has the yellow board they used early on. This pre was apparently at Atma-Sphere recently where it received; new filter caps, HV regulated power supplies, fast rectifiers, the latest 3.1 version volume attenuator, main power transformer, and state of the art copper CuTF V-Cap coupling caps, as well as a full cleaning of all controls and input/output connections. The price is reasonable but I have no idea where something like that would fall between the MP-3 and MP-1. It would have to offer something above the MP-3 I owned for me to consider trying it.

Grannyring, your issue doesn't seem to me to be a ground loop issue, as it occurs even when the preamp is unplugged from the AC outlet (and with no source components connected). Therefore I'm not at all certain that a Jensen transformer would solve the problem, which I'm frankly out of ideas on.

For anyone else who may be able to contribute ideas on Grannyring's issue, it was discussed here. Note that multiple sets of interconnect cables were tried, as well as both the Dude and Lightspeed preamps. Yet the problem goes away when the inputs to the amp are disconnected, and the problem did not occur until the previous speakers, which were electrostatics, were replaced with passive speakers.

Best regards,
-- Al

My Dude works fine with my low gain power amp. But when it was used with a pair of high gain tube monoblocks, I could hear some humming noises. So I got rid of the ground loop by floating the signal ground from the AC ground at the power amp, but keeping the chassis connected to the AC ground for safety. It has been quiet since then.